Multilayer structure having a layer based on polyamide and on HDPE

ABSTRACT

The present invention relates to a structure successively comprising: a first layer of high density polyethylene (HDPE), a tie layer, a second layer of EVOH or of a blend based on EVOH, optionally a tie layer, a third layer of a blend comprising, by weight, the total being 100%: 50 to 90% of polyamide (A) having a conversion temperature of at most 230° C., 1 to 30% of high density polyethylene (HDPE), 5 to 30% of an impact modifier chosen from elastomers and very low density polyethylenes, at least one of the HDPE and of the impact modifier being functionalized, in all or part, the layers being coextrudable. The present invention also relates to devices for the transfer or storage of fluids and more particularly to pipes, tanks, conduits, bottles and containers composed of the above structure in which the layer of the blend of polyamide (A) and of HDPE is in direct contact with the fluid present or transported

This application claims benefit, under U.S.C. § 119(a) of FrenchNational Applications Number 04.06635, filed Jun. 18, 2004; and04.10391, filed Oct. 01, 2004 ; and also claims benefit, under U.S.C. §119(e) of U.S. provisional applications 60/585494, filed Jul. 2, 2004and 60/631933 filed Nov. 30, 2004.

FIELD OF THE INVENTION

The present invention relates to a multilayer structure having a layerbased on polyamide and on HDPE (high density polyethylene). It alsorelates to a tank composed of this structure having this layer in directcontact with the fluid contained in the tank. The layer based onpolyamide and on HDPE of the structures of the invention constitutes oneof the faces of the structure, that is to say that it is not inside thestructure (sandwich). These structures are of use in the manufacture ofdevices for the transfer or storage of fluids and more particularlypipes, tanks, tank conduits, that is to say the pipe which is used tofill the tank, bottles and containers in which the layer based onpolyamide and on HDPE is in contact with the fluid. It is of particularuse for tanks.

The invention is of use for a fluid, such as motor vehicle petrol, bypreventing losses through the structure, so as not to pollute theenvironment. It is also of use for liquids comprising volatilesubstances by preventing depletion of the liquid in this volatilesubstance. The invention is also of use for the liquid coolant of theengines, for the oil and for the fluid of the air-conditioning system.

BACKGROUND OF THE INVENTION

Patent EP 742 236 discloses petrol tanks composed of five layers, whichare respectively:

high density polyethylene (HDPE);

a tie;

a polyamide (PA) or a copolymer having ethylene units and vinyl alcoholunits (EVOH);

a tie;

HDPE.

-   A sixth layer can be added between one of the tie layers and one of    the HDPE layers. This sixth layer is composed, for example, of the    manufacturing scrap material resulting from the forming of the tanks    or, in a much smaller amount, of tanks which have failed    specification. This scrap material and these tanks which have failed    specification are ground. This ground material is subsequently    remelted and directly extruded on the plant for the coextrusion of    the tanks. This ground material might also be melted and    regranulated by an extrusion device, such as a twin-screw or    single-screw extruder, before being reused.

According to one alternative form, the recycled product can be blendedwith the HDPE of the two outermost layers of the tank. It is possible,for example, to blend the granules of recycled product with the granulesof virgin HDPE of these two layers. It is also possible to use anycombination of these recycling operations. The level of recycledmaterial can represent up to 50% of the total weight of the tank.

U.S. Pat. No. 6,177,162 discloses a tube comprising an inner layercomprising a blend of polyamide and of polyolefin with a polyamidematrix and an outer layer comprising a polyamide. These polyamide-basedtubes are of use for the transportation of petrol and more particularlyfor conveying the petrol from the tank of the motor vehicle to theengine and also, but with a larger diameter, for the transportation ofhydrocarbons in service stations between the distribution pumps and theunderground storage reservoirs.

According to another form of the invention, it is possible to position,between the inner and outer layers, a layer of a polymer comprisingethylene units and vinyl alcohol units (EVOH). Use is advantageouslymade of the structure: inner layer/EVOH/tie/outer layer.

The tanks disclosed in EP 742 236, and which do not have the barrierlayer in direct contact with the petrol, certainly have barrierproperties but they are not sufficient when very low petrol losses arebeing looked for. EP 731 308 discloses pipes which have their outerlayer made of polyamide and the barrier layer in direct contact with thepetrol; the layer made of polyamide is necessary for the mechanicalstrength of the combined product.

Patent Application 2005089701 discloses a structure successivelycomprising:

a first layer of high density polyethylene (HDPE),

a tie layer,

a second layer of EVOH or of a blend based on EVOH,

optionally a third layer of polyamide or of a blend of polyamide and ofpolyolefin. Numerous blends of polyamide and of polyolefin which canconstitute the third layer are described in this patent. It has now beenfound that this third layer is necessary and, furthermore, that it hasto comprise HDPE in order to obtain good barrier properties.Furthermore, the conversion temperature of the polyamide of this thirdlayer must not be too high in order not to be too far from that of theEVOH.

SUMMARY OF THE INVENTION

The present invention relates to a structure successively comprising:

-   a first layer of high density polyethylene (HDPE),-   a tie layer,-   a second layer of EVOH or of a blend based on EVOH,-   optionally a tie layer,-   a third layer of a blend comprising, by weight, the total being    100%:

50 to 90% of polyamide (A) having a conversion temperature of at most230° C.,

1 to 30% of high density polyethylene (HDPE),

5 to 30% of an impact modifier chosen from elastomers and very lowdensity polyethylenes,

at least one of the HDPE and of the impact modifier beingfunctionalized, in all or part, the layers being coextrudable.

Use may be made of a blend of different HDPEs. It can be a blend ofdifferent nonfunctionalized HDPEs, of a nonfunctionalized HDPE and ofthe same HDPE but functionalized, of a nonfunctionalized HDPE and ofanother HDPE but functionalized or of two different grafted HDPEs, orany combination of these possibilities.

Use may be made of a blend of different impact modifiers. It can be ablend of different nonfunctionalized impact modifiers, of anonfunctionalized impact modifier and of the same impact modifier butfunctionalized, of a nonfunctionalized impact modifier and of anotherimpact modifier but functionalized, of two different functionalizedimpact modifiers or of a functionalized impact modifier and of afunctionalized HDPE with optionally a nonfunctionalized impact modifierand optionally a nonfunctionalized HDPE, or any combination of thesepossibilities.

The layers are “coextrudable”, meaning that they are in the samerheology range to form, for example, a parison which can be blow-mouldedto form a hollow body or an extruded tube.

The proportion of functional groups of the HDPE and/or of the impactmodifier must be sufficient for the layer based on polyamide (A) and onHDPE to have mechanical strength but not too great in order for theviscosity not to be so high that the layer is no longer coextrudable.

The present invention also relates to devices for the transfer orstorage of fluids and more particularly to pipes, tanks, conduits,bottles and containers composed of the above structure in which thelayer of the blend of polyamide (A) and of HDPE is in direct contactwith the fluid present or transported. These devices can be manufacturedby conventional techniques of the industry of thermoplastic polymers,such as coextrusion and coextrusion blow-moulding.

DETAILED DESCRIPTION OF THE INVENTION

As regards the first layer, high density polyethylene (HDPE) isdescribed in Kirk-Othmer, 4th edition, Vol. 17, pages 704 and 724-725.It is, according to ASTM D 1248-84, an ethylene polymer having a densityof at least 0.940. The name HDPE relates both to ethylene homopolymersand to copolymers of ethylene with small proportions of α-olefin. Thedensity is advantageously between 0.940 and 0.965. In the presentinvention, the MFI of the HDPE is advantageously between 0.1 and 50.Mention may be made, as examples, of Eltex B 2008®, with a density of0.958 and an MFI of 0.9 (in g/10 min at 190° C. under 2.16 kg),Finathene® MS201B from Fina and Lupolen® 4261 AQ from BASF. As regardsthe high density polyethylene of the first layer, its density isadvantageously between 0.940 and 0.965 and the MFI is between 0.1 and 5g/10 min. (190° C., 5 kg).

As regards the second layer, the EVOH copolymer is also known assaponified vinyl acetate/ethylene copolymer. The saponified vinylacetate/ethylene copolymer to be employed according to the presentinvention is a copolymer having an ethylene content of 20 to 70 mol %,preferably of 25 to 70 mol %, the degree of saponification of its vinylacetate component being not less than 95 mol %. With an ethylene contentof less than 20 mol %, the barrier properties under conditions of highhumidity are not as great as would be desired, while an ethylene contentexceeding 70 mol % leads to declines in the barrier properties. When thedegree of saponification or of hydrolysis is less than 95 mol %, thebarrier properties are lost.

The term “barrier properties” is understood to mean impermeability togases and to liquids and in particular to oxygen and to petrol for motorvehicles. The invention relates more particularly to the barrier topetrol for motor vehicles.

Among these saponified copolymers, those which have melt flow indices inthe range from 0.5 to 100 g/10 minutes are of particular use.Advantageously, the MFI is chosen between 5 and 30 (g/10 min at 230° C.under 2.16 kg); “MFI” is the abbreviation for Melt Flow Index.

It is understood that this saponified copolymer can comprise smallproportions of other comonomer ingredients, including α-olefins, such aspropylene, isobutene, α-octene, α-dodecene, α-octadecene, and the like,unsaturated carboxylic acids or their salts, partial alkyl esters,complete alkyl esters, nitrites, amides and anhydrides of the saidacids, and unsaturated sulphonic acids or their salts.

With regard to the blends based on EVOH, they are such that the EVOHforms the matrix, that is to say that it represents at least 40% byweight of the blend and preferably at least 50%. The other constituentsof the blend are chosen from polyolefins, polyamides or impact modifierswhich are optionally functionalized. The impact modifier can be chosenfrom elastomers, copolymers of ethylene and of an olefin having 4 to 10carbon atoms (for example, ethylene-octene copolymers), and very lowdensity polyethylenes. Mention may be made, as examples of elastomers,of EPR and EPDM. EPR (abbreviation for Ethylene-Propylene Rubber)denotes ethylene-propylene elastomers and EPDM denotesethylene-propylene-diene monomer elastomers.

As first example of these blends based on EVOH of the second layer,mention may be made of the compositions comprising (by weight):

55 to 99.5 parts of EVOH copolymer,

0.5 to 45 parts of polypropylene and of compatibilizing agent, theirproportions being such that the ratio of the amount of polypropylene tothe amount of compatibilizing agent is between 1 and 5.

-   Advantageously, the ratio of the MFI of the EVOH to the MFI of the    polypropylene is greater than 5 and preferably between 5 and 25.    Advantageously, the MFI of the polypropylene is between 0.5 and 3    (in g/10 min at 230° C. under 2.16 kg). According to an advantageous    form, the compatibilizing agent is a polyethylene carrying polyamide    grafts and it results from the reaction (i) of a copolymer of    ethylene and of a grafted or copolymerized unsaturated monomer X    with (ii) a polyamide. The copolymer of ethylene and of a grafted or    copolymerized unsaturated monomer X is such that X is copolymerized    and it can be chosen from ethylene/maleic anhydride copolymers and    ethylene/alkyl (meth)acrylate/maleic anhydride copolymers, these    copolymers comprising from 0.2 to 10% by weight of maleic anhydride    and from 0 to 40% by weight of alkyl (meth)acrylate.

According to another advantageous form, the compatibilizing agent is apolypropylene carrying polyamide grafts which results form the reaction(i) of a homopolymer or of a copolymer of propylene comprising a graftedor copolymerized unsaturated monomer X with (ii) a polyamide.Advantageously, X is grafted. The monomer X is advantageously anunsaturated carboxylic acid anhydride, such as, for example, maleicanhydride.

As second example of these blends based on EVOH of the second layer,mention may be made of the compositions comprising:

50 to 98% by weight of an EVOH copolymer,

1 to 50% by weight of a polyethylene,

1 to 15% by weight of a compatibilizing agent composed of a blend of anLLDPE polyethylene or metallocene polyethylene and of a polymer chosenfrom elastomers, very low density polyethylenes and metallocenepolyethylenes, the blend being cografted by an unsaturated carboxylicacid or a functional derivative of this acid.

Advantageously, the compatibilizing agent is such that the MFI₁₀/MFI₂ratio is between 5 and 20, where MFI₂ is the melt flow index at 190° C.under a load of 2.16 kg, measured according to ASTM D1238, and MFI₁₀ isthe melt flow index at 190° C. under a load of 10 kg, according to ASTMD1238.

As third example of these blends based on EVOH of the second layer,mention may be made of the compositions comprising:

50 to 98% by weight of an EVOH copolymer,

1 to 50% by weight of an ethylene/alkyl (meth)acrylate copolymer,

1 to 15% by weight of a compatibilizing agent resulting from thereaction (i) of a copolymer of ethylene and of a grafted orcopolymerized unsaturated monomer X with (ii) a copolyamide.

Advantageously, the copolymer of ethylene and of a grafted orcopolymerized unsaturated monomer X is such that X is copolymerized andthis is a copolymer of ethylene and of maleic anhydride or a copolymerof ethylene, of an alkyl (meth)acrylate and of maleic anhydride.

Advantageously, these copolymers comprise from 0.2 to 10% by weight ofmaleic anhydride and from 0 to 40% by weight of alkyl (meth) acrylate.

As fourth example of these blends based on EVOH of the second layer,mention may be made of the compositions comprising:

50 to 98% by weight of an EVOH copolymer,

2 to 50% by weight of an elastomer which is optionally functionalized inall or part or of a blend of a functionalized elastomer and of anothernonfunctionalized elastomer.

As regards the blend of polyamide (A) and of HDPE of the third layer,the term “conversion temperature” is understood to mean the temperatureat which it is coextruded with the material of the other layers and/orcoextruded and blow-moulded with the material of the other layers. Forsemicrystalline polyamides, this is a temperature above the meltingpoint (usually denoted by M.p.) and, for amorphous polyamides, this is,of course, a temperature above the Tg (glass transition temperature).The term “above” is understood to mean generally a difference of 10 to50° C.

This polyamide (A) is chosen from the products which comprise unitsoriginating:

from one or more amino acids, such as aminocaproic acid,7-aminoheptanoic acid, 11-aminoundecanoic acid and 12-aminododecanoicacid, or from one or more lactams, such as caprolactam, enantholactamand lauryllactam;

from one or more salts or mixtures of diamines with diacids. Mention maybe made, as examples of diacids, of isophthalic acid, terephthalic acidor dicarboxylic acids having from 6 to 18 carbon atoms, such as adipicacid, azelaic acid, suberic acid, sebacic acid and dodecanedicarboxylicacid. The diamine can be an aliphatic diamine having from 6 to 18 atoms,it can be an arylic and/or saturated cyclic diamine. Mention may bemade, as examples, of hexamethylenediamine, piperazine,tetramethylenediamine, octamethylenediamine, decamethylenediamine,dodecamethylenediamine, 1,5-diaminohexane,2,2,4-trimethyl-1,6-diaminohexane, polyoldiamines, isophoronediamine(IPD), methylpentamethylenediamine (MPDM), bis(aminocyclohexyl)methane(BACM), or bis(3-methyl-4aminocyclohexyl)methane (BMACM).

Use may also advantageously be made of copolyamides. Mention may be madeof the copolyamides resulting from the condensation of at least twoα,ω-aminocarboxylic acids or of two lactams or of a lactam and of anα,ω-aminocarboxylic acid. Mention may also be made of the copolyamidesresulting from the condensation of at least one α-ω-aminocarboxylic acid(or one lactam), at least one diamine and at least one dicarboxylicacid.

Mention may be made, as examples of lactams, of those which have from 3to 12 carbon atoms on the main ring and which can be substituted.Mention may be made, for example, of β,β-dimethylpropiolactam,α,α-dimethylpropiolactam, amylolactam, caprolactam, capryllactam andlauryllactam.

Mention may be made, as examples of α,ω-aminocarboxylic acids, ofaminoundecanoic acid and aminododecanoic acid. Mention may be made, asexamples of dicarboxylic acids, of adipic acid, sebacic acid,isophthalic acid, butanedioic acid, 1,4-cyclohexanedicarboxylic acid,terephthalic acid, the sodium or lithium salt of sulphoisophthalic acid,dimerized fatty acids (these dimerized fatty acids have a dimer contentof at least 98% and are preferably hydrogenated) and dodecanedioic acidHOOC-(CH₂)₁₀-COOH.

Mention may be made, as examples of copolyamides, of copolymers ofcaprolactam and of lauryllactam (PA 6/12), copolymers of caprolactam, ofadipic acid and of hexamethylenediamine (PA 6/6-6), copolymers ofcaprolactam, of lauryllactam, of adipic acid and of hexamethylenediamine(PA 6/12/6-6), copolymers of caprolactam, of lauryllactam, of11-aminoundecanoic acid, of azelaic acid and of hexamethylenediamine (PA6/6-9/11/12), copolymers of caprolactam, of lauryllactam, of11-aminoundecanoic acid, of adipic acid and of hexamethylenediamine (PA6/6-6/11/12) or copolymers of lauryllactam, of azelaic acid and ofhexamethylenediamine (PA 6-9/12).

-   All these polyamides (A) are known per se and are manufactured    according to the usual processes for polyamides.

Advantageously, the copolyamide is chosen from PA 6/12 and PA 6/6-6.

Polyamide blends can be used. Advantageously, the relative viscosity,measured in 96% sulphuric acid, is between 2 and 5.

It would not be departing from the scope of the invention to replace aportion of the polyamide (A) with a copolymer comprising polyamideblocks and polyether blocks, that is to say to use a blend comprising atleast one of the above polyamides and at least one copolymer comprisingpolyamide blocks and polyether blocks.

The copolymers comprising polyamide blocks and polyether blocks resultfrom the copolycondensation of polyamide sequences comprising reactiveends with polyether sequences comprising reactive ends, such as, interalia:

1) Polyamide sequences comprising diamine chain ends withpolyoxyalkylene sequences comprising dicarboxyl chain ends.

2) Polyamide sequences comprising dicarboxyl chain ends withpolyoxyalkylene sequences comprising diamine chain ends obtained bycyanoethylation and hydrogenation of aliphatic α,ω-dihydroxylatedpolyoxyalkylene sequences, known as polyetherdiols.

3) Polyamide sequences comprising dicarboxyl chain ends withpolyetherdiols, the products obtained being, in this specific case,polyetheresteramides. Use is advantageously made of these copolymers.

The polyamide sequences comprising dicarboxyl chain ends originate, forexample, from the condensation of α,ω-aminocarboxylic acids, of lactamsor of dicarboxylic acids and diamines in the presence of achain-limiting dicarboxylic acid.

The polyether can, for example, be a polyethylene glycol (PEG), apolypropylene glycol (PPG) or a polytetramethylene glycol (PTMG). Thelatter is also known as polytetrahydrofuran (PTHF).

The number-average molar mass {overscore (Mn)} of the polyamidesequences is between 300 and 15 000 and preferably between 600 and 5000.The mass {overscore (Mn)} of the polyether sequences is between 100 and6000 and preferably between 200 and 3000.

The polymers comprising polyamide blocks and polyether blocks can alsocomprise randomly distributed units. These polymers can be prepared bythe simultaneous reaction of the polyether and of the precursors of thepolyamide blocks.

For example, polyetherdiol, a lactam (or an α,ω-amino acid) and achain-limiting diacid can be reacted in the presence of a small amountof water. A polymer is obtained which has essentially polyether blocksand polyamide blocks, the latter being of highly variable length, butalso the various reactants which have reacted randomly, which aredistributed statistically along the polymer chain.

These polymers comprising polyamide blocks and polyether blocks, whetherthey originate from the copolycondensation of polyamide and polyethersequences prepared beforehand or from a one-stage reaction, exhibit, forexample, Shore D hardnesses which can be between 20 and 75 andadvantageously between 30 and 70 and an intrinsic viscosity of between0.8 and 2.5, measured in meta-cresol at 250° C. for an initialconcentration of 0.8 g/100 ml. The MFI values can be between 5 and 50(235° C. under a load of 1 kg).

The polyetherdiol blocks are either used as is and copolycondensed withpolyamide blocks comprising carboxyl ends or they are aminated, in orderto be converted into polyetherdiamines, and condensed with polyamideblocks comprising carboxyl ends. They can also be blended with polyamideprecursors and a chain-limiting agent in order to prepare polymerscomprising polyamide blocks and polyether blocks having statisticallydistributed units.

Polymers comprising polyamide and polyether blocks are disclosed in U.S.Pat. No. 4,331,786, U.S. Pat. No. 4,115,475, U.S. Pat. No. 4,195,015,U.S. Pat. No. 4,839,441, U.S. Pat. No. 4,864,014, U.S. Pat. No.4,230,838 and U.S. Pat. No. 4,332,920.

The ratio of the amount of copolymer comprising polyamide blocks andpolyether blocks to the amount of polyamide is advantageously between10/90 and 60/40, by weight.

As regards the HDPE of the third layer, its density is advantageouslybetween 0.940 and 0.965 and the MFI between 1 and 10 g/10 min. (190° C.,5 kg).

As regards the impact modifier and first the elastomers, mention may bemade of SBS, SIS and SEBS block polymers and ethylene/propylene (EPR) orethylene/propylene/diene (EPDM) elastomers. With regard to the very lowdensity polyethylenes, these are, for example, metallocenes with adensity, for example, between 0.860 and 0.900.

Use is advantageously made of an ethylene/propylene (EPR) orethylene/propylene/diene (EPDM) elastomer. The functionalization can beintroduced by grafting or copolymerization with an unsaturatedcarboxylic acid. It would not be departing from the scope of theinvention to use a functional derivative of this acid. Examples ofunsaturated carboxylic acids are those having 2 to 20 carbon atoms, suchas acrylic acid, methacrylic acid, maleic acid, fumaric acid anditaconic acid. The functional derivatives of these acids comprise, forexample, the anhydrides, the ester derivatives, the amide derivatives,the imide derivatives and the metal salts (such as the alkali metalsalts) of the unsaturated carboxylic acids.

Unsaturated dicarboxylic acids having 4 to 10 carbon atoms and theirfunctional derivatives, particularly their anhydrides, are particularlypreferred grafting monomers. These grafting monomers comprise, forexample, maleic acid, fumaric acid, itaconic acid, citraconic acid,allylsuccinic acid, cyclohex-4-ene-1,2-dicarboxylic acid,4-methylcyclohex-4-ene-1,2-dicarboxylic acid,bicyclo[2.2.1]hept-5-ene-2,3-dicarboxylic acid,x-methylbicyclo[2.2.1]hept-5-ene-2,3-dicarboxylic acid, maleicanhydride, itaconic anhydride, citraconic anhydride, allylsuccinicanhydride, cyclohex-4-ene-1,2-dicarboxylic anhydride,4-methylcyclohex-4-ene-1,2-dicarboxylic anhydride,bicyclo[2.2.1]hept-5-ene-2,3-dicarboxylic anhydride andx-methylbicyclo[2.2.1]hept-5-ene-2,3-dicarboxylic anhydride. Use isadvantageously made of maleic anhydride.

Various known processes can be used to graft a grafting monomer to apolymer. For example, this can be carried out by heating the polymers athigh temperature, approximately 150° to approximately 300° C., in thepresence or in the absence of a solvent and with or without a radicalgenerator. The amount of the grafting monomer can be appropriatelychosen but it is preferably from 0.01 to 10%, better still from 600 ppmto 2%, with respect to the weight of the polymer to which the graft isattached.

It is possible to graft, in all or part, the impact modifier and toblend it with the HDPE. It is possible to graft the HDPE, in all orpart, and to blend it with the impact modifier. It is also possibleseparately to graft, in all or part, the impact modifier, to graft theHDPE, in all or part, and then to blend the two grafted products. It isalso possible to blend the impact modifier with the HDPE and to graft,in all or part, the blend.

The proportion of functionalized HDPE and/or of functionalized modifierwith respect to the combined functionalized or nonfunctionalized HDPEand functionalized or nonfunctionalized impact modifier can be (byweight) between 0 and 70%, advantageously between 5 and 60% andpreferably between 20 and 60%.

According to one form of the invention, the HDPE is not functionalizedand the impact modifier is functionalized in all or part.

The proportions of the blend of the third layer are advantageously, thetotal being 100%:

-   55 to 80% of polyamide (A),-   10 to 20% of high density polyethylene (HDPE),-   10 to 30% of impact modifier.

The blends of the third layer can be prepared by blending the variousconstituents in the molten state in conventional devices of thethermoplastic polymer industry.

The first layer can be composed of a layer of virgin HDPE and of a layerof recycled polymers (also referred to as regrind layer) originatingfrom scrap material during the manufacture of the transfer or storagedevices or from these devices which have failed specification, as isexplained in the abovementioned prior art. This layer of recycledpolymers is situated on the side of the tie layer. In the continuationof the text, these two layers will be denoted for simplicity by the term“first layer”. Functionalized polyolefins can be added to this layer ofrecycled polymers in a proportion which can, for example, be between 0.1and 10% by weight. These functionalized polyolefins are advantageouslychosen from the ties. Either HDPE or functionalized polyolefins or ablend of the two can be added to this layer of recycled polymers.

The thickness of the first layer can be between 2 and 10 mm, that of thesecond between 30 and 500 μm and that of the third between 500 μm and 4mm. As regards the tanks, the overall thickness is usually between 3 and10 mm.

As example of tie, mention may be made of functionalized polyolefins.The tie between the first and the second layer and that between thesecond and the third layer can be identical or different. In thefollowing descriptions of ties, the term “polyethylene” denotes bothhomopolymers and copolymers.

As first tie example, mention may be made of a blend of a polyethylene(C1) and of a polymer (C2) chosen from elastomers, very low densitypolyethylenes and ethylene copolymers, the blend (C1)+(C2) beingcografted by an unsaturated carboxylic acid.

According to an alternative form, mention may be made of a blend (i) ofa polymer (C2) chosen from elastomers, very low density polyethylenesand ethylene copolymers, (C2) being grafted by an unsaturated carboxylicacid, and (ii) of a polymer (C2) chosen from elastomers, very lowdensity polyethylenes and ethylene copolymers.

As second tie example, mention may be made of the blends comprising:

5 to 30 parts of a polymer (D) itself comprising a blend of apolyethylene (D1) with a density of between 0.910 and 0.940 and of apolymer (D2) chosen from elastomers, very low density polyethylenes andmetallocene polyethylenes, the blend (D1)+(D2) being cografted by anunsaturated carboxylic acid,

95 to 70 parts of a polyethylene (E) with a density of between 0.910 and0.930,

the blend of (D) and (E) being such that:

-   -   its density is between 0.910 and 0.930,    -   the content of grafted unsaturated carboxylic acid is between 30        and 10 000 ppm,    -   the MFI (ASTM D 1238, 190° C., 2.16 kg) is between 0.1 and 3        g/10 min, the MFI denoting the melt flow index.

The density of the tie is advantageously between 0.915 and 0.920.Advantageously, (D1) and (E) are LLDPEs; preferably, they have the samecomonomer. This comonomer can be chosen from 1-hexene, 1-octene and1-butene.

As third tie example, mention may be made of the blends comprising:

5 to 30 parts of a polymer (F) itself comprising a blend of apolyethylene (F1) with a density of between 0.935 and 0.980 and of apolymer (F2) chosen from elastomers, very low density polyethylenes andethylene copolymers, the blend (F1)+(F2) being cografted by anunsaturated carboxylic acid,

95 to 70 parts of a polyethylene (G) with a density of between 0.930 and0.950,

the blend of (F) and (G) being such that:

-   -   its density is between 0.930 and 0.950 and advantageously        between 0.930 and 0.940,    -   the content of grafted unsaturated carboxylic acid is between 30        and 10 000 ppm,    -   the MFI (melt flow index), measured according to ASTM D 1238 at        190° C. and 2.16 kg, is between 5 and 100.

As fourth tie example, mention may be made of polyethylene grafted bymaleic anhydride having an MFI of 0.1 to 3 and a density of between0.920 and 0.930 and which comprises 2 to 40% by weight of materialswhich are insoluble in n-decane at 90° C. In order to determine thematerials which are insoluble in n-decane, the grafted polyethylene isdissolved in n-decane at 140° C., is cooled to 90° C. and productsprecipitate; it is then filtered and the level of insoluble materials isthe percentage by weight which precipitates and is collected byfiltration at 90° C. If the level is between 2 and 40%, the tie has goodresistance to petrol.

Advantageously, the grafted polyethylene is diluted in an ungraftedpolyethylene such that the tie is a blend of 2 to 30 parts of a graftedpolyethylene with a density of between 0.930 and 0.980 and of 70 to 98parts of an ungrafted polyethylene with a density of between 0.910 and0.940, preferably 0.915 and 0.935.

As fifth tie example, mention may be made of the blends comprising:

-   -   50 to 100 parts of a polyethylene (J) homo- or copolymer with a        density of greater than or equal to 0.9,    -   0 to 50 parts of a polymer (K) chosen from (K1) polypropylene        homo- or copolymer, (K2) poly(1-butene) homo- or copolymer and        (K3) polystyrene homo- or copolymer,    -   the amount of (J)+(K) being 100 parts,    -   the blend of (J) and (K) being grafted by at least 0.5% by        weight of a functional monomer,    -   this grafted blend being itself diluted in at least one        polyethylene homo- or copolymer (L) or in at least one polymer        with an elastomeric nature (M) or in a blend of (L) and (M).

According to one form of the invention, (J) is an LLDPE with a densityof 0.910 to 0.930, the comonomer having from 4 to 8 carbon atoms.According to another form of the invention, (K) is an HDPE,advantageously with a density of at least 0.945 and preferably of 0.950to 0.980.

Advantageously, the functional monomer is maleic anhydride and itscontent is from 1 to 5% by weight of (J)+(K).

Advantageously, (L) is an LLDPE, the comonomer of which has from 4 to 8carbon atoms, and its density is preferably at least 0.9 and preferably0.910 to 0.930.

Advantageously, the amount of (L) or (M) or (L)+(M) is from 97 to 75parts per 3 to 25 parts of (J)+(K), the amount of (J)+(K)+(L)+(M) being100 parts.

As sixth tie example, mention may be made of the blends composed of apolyethylene of HDPE, LLDPE, VLDPE or LDPE type, 5 to 35% of a graftedmetallocene polyethylene and 0 to 35% of an elastomer, the total being100%.

As seventh tie example, mention may be made of the blends comprising:

at least one polyethylene or one ethylene copolymer,

at least one polymer chosen from polypropylene or a propylene copolymer,poly(1-butene) homo- or copolymer, or polystyrene homo- or copolymer,and preferably polypropylene,

this blend being grafted by a functional monomer and this grafted blendbeing itself optionally diluted in at least one polyolefin or in atleast one polymer with an elastomeric nature or in their blend. In thepreceding blend which is grafted, the polyethylene advantageouslyrepresents at least 50% of this blend and preferably 60 to 90% byweight.

Advantageously, the functional monomer is chosen from carboxylic acidsand their derivatives, acid chlorides, isocyanates, oxazolines,epoxides, amines or hydroxides and preferably unsaturated dicarboxylicacid anhydrides.

As eighth tie example, mention may be made of the blends comprising:

at least one LLDPE or VLDPE polyethylene,

at least one ethylene-based elastomer chosen from ethylene/propylenecopolymers and ethylene/butene copolymers,

this blend of polyethylene and of elastomer being grafted by anunsaturated carboxylic acid or a functional derivative of this acid,

this cografted blend being optionally diluted in a polymer chosen frompolyethylene homo- or copolymers and styrene block copolymers,

the tie having

-   (a) an ethylene content which is not less than 70 mol %,-   (b) a content of carboxylic acid or of its derivative of 0.01 to 10%    by weight of the tie, and-   (c) an MFI₁₀/MFI₂ ratio of 5 to 20, where MFI₂ is the melt flow    index at 190° C. under a load of 2.16 kg, measured according to ASTM    D1238, and MFI₁₀ is the melt flow index at 190° C. under a load of    10 kg, according to ASTM D1238.

The various layers of the structure of the invention, including the tielayers, can additionally comprise at least one additive chosen from:

-   -   fillers (inorganic, flame-retardant, conductive, and the like),    -   nanofillers, such as, for example, nanoclays,    -   nanocomposites,    -   fibres,    -   dyes,    -   pigments,    -   optical brighteners,    -   antioxidants,    -   nucleating agents,    -   UV stabilizers.

EXAMPLES

Polymers used:

PA A1: Terpolymer of caprolactam (L6), adipic acid (AA) andhexamethylenediamine (HMDA) possessing an L6/[AA+HMDA] ratio by mass of85/15 and a “viscosity number” of 186 according to Standard ISO 307.

PA A2: Copolymer of caprolactam and of lauryllactam possessing a monomercomposition by weight of 70/30 and an intrinsic viscosity (measured at20° C. for a concentration of 0.5 g per 100 ml of meta-cresol) of 1.3dl/g.

PA A3: Copolymer of caprolactam and of lauryllactam possessing a meltingpoint of 190° C. and a melt flow index of 120 according to Standard ISO1133, measured under the conditions: 275° C. under a load of 5 kg.

PA A4: Lauryllactam homopolymer possessing an intrinsic viscosity(measured at 20° C. for a concentration of 0.5 g per 100 ml ofmeta-cresol) of 1.55 to 1.74 dl/g.

PA A5: 11-Aminoundecanoic acid homopolymer possessing an intrinsicviscosity (measured at 20° C. for a concentration of 0.5 g per 100 ml ofmeta-cresol) of 1.35 to 1.52 dl/g.

PA A6 (10.10): Equimolar copolymer of sebacic acid (SA) and ofdecanediamine (DA) possessing an intrinsic viscosity (measured at 20° C.for a concentration of 0.5 g per 100 ml of meta-cresol) of 1.4 dl/g.

PA A7 (MXD.10): Equimolar copolymer of meta-xylylenediamine (MXD) and ofsebacic acid (SA) possessing an intrinsic viscosity (measured at 20° C.for a concentration of 0.5 g per 100 ml of meta-cresol) of 1.4 dl/g.

PA A8 (MXD.12): Equimolar copolymer of meta-xylylenediamine (MXD) and ofdodecanedioic acid (DDA) possessing an intrinsic viscosity (measured at20° C. for a concentration of 0.5 g per 100 ml of meta-cresol) of 1.4dl/g.

PE 1: Polyethylene possessing a density of 0.952 according to StandardISO 1183 and a melt flow index of 23 according to Standard ISO 1133,measured under the conditions: 190° C. under a load of 2.16 kg.

PE 2: Polyethylene having a density of 0.949 according to Standard ISO1183 and a melt flow index of 8 g/10 min according to Standard ISO 1133,measured under the conditions: 190° C. under a load of 2.16 kg.

P1: Terpolymer of ethylene, of propylene and of diene monomer possessinga density of 0.89 and a Mooney viscosity (ML, 1+4, 125° C.) of 30 andgrafted by maleic anhydride at a level of 1%.

P2: Terpolymer of ethylene, of propylene and of diene monomer possessinga Mooney viscosity of 30 under the conditions ML (1+4) 100° C.

EVOH: Copolymer of ethylene and of p2yl alcohol possessing an ethylenefraction by weight of 29% and a melt flow index of 3.2, measuredaccording to Standard ISO 1133 under the following conditions: 210° C.under a load of 2.16 kg.

T1 (Orevac): Polyethylene grafted by 3000 ppm of maleic anhydride andpossessing a melt flow index of 1, measured according to Standard ASTM1238 under the following conditions: 190° C. under a load of 2.16 kg.

Alloy 1: Compatibilized blend of PA and of PP possessing an M.p. of 255°C. and a melt flow index of 15, measured according to Standard ISO 1133under the following conditions: 275° C. under a load of 2.16 kg, sold bythe Applicant Company under the reference Orgalloy® RS6600.

Alloy 2: Compatibilized blend of PA and of PE possessing an M.p. of 225°C. but a conversion temperature of 250° C. and a melt flow index of 2,measured according to Standard ISO 1133 under the following conditions:235° C. under a load of 2.16 kg, sold by the Applicant Company under thereference Orgalloy® LE 6000.

Alloy 3: Compatibilized blend of PA and of PE possessing an M.p. of 195°C. and a melt flow index of 3, measured according to Standard ISO 1133under the following conditions: 235° C. under a load of 2.16 kg, sold bythe Applicant Company under reference Orgalloy® LEC601.

Preparation of the alloys of polyamide and of polyolefin:

The alloys of polyamide and of polyolefin are prepared using acorotating twin-screw extruder of Werner & Pfleiderer ZSK 40 type(diameter=40 mm, L=40D).

Preparation of multilayer hollow bodies by coextrusion blow-moulding:

Multilayer bottles are prepared using a Bekum coextrusion blow-mouldingline equipped with 5 extruders, the barrels of which are regulated at220° C., unless otherwise mentioned. The blow-moulded structures are oftwo types:

-   four-layer structures described as follows, from the inside    outwards:-   1. Alloy of polyamide and of polyolefin: Thickness: 30% of the    overall thickness (extruder 1)-   2. EVOH: Thickness: 5% of the overall thickness (extruder 2)-   3. T1: Thickness: 5% of the overall thickness (extruder 3)-   4. PE2: Thickness: 60% of the overall thickness (extruder 4)-   The overall thickness is 3 mm on average.    five-layer structures described as follows, from the inside    outwards:-   1. Alloy of polyamide and of polyolefin: Thickness: 30% of the    overall thickness (extruder 1)-   2. Ti: Thickness: 5% of the overall thickness (extruder 5)-   3. EVOH: Thickness: 5% of the overall thickness (extruder 2)-   4. T1: Thickness: 5% of the overall thickness (extruder 3)-   5. PE2: Thickness: 55% of the overall thickness (extruder 4)-   The overall thickness is 3 mm on average.

Impact strength of the bottles:

The blow-moulded bottles, conditioned beforehand at −40° C., are testedon one of their flat surfaces with regard to impact strength under thefollowing conditions: T=−40° C. and impact speed=4.3 m/s.

The force-displacement curve resulting from this test makes it possibleto calculate the impact strength of the multilayer bottle.

Results:

Examples 1 to 3

3 four-layer bottles, the structures of which are collated in the tablebelow, were extruded blow-moulded on the Bekum extrusion line. Example1* Example 2** (comparative) (comparative) Example 3 Alloy 1 Alloy 2Alloy 3 EVOH EVOH EVOH T1 T1 T1 Structure PE2 PE2 PE2 Quality of theLack of coextrusion Lack of coextrusion Correct coextrusion*Extruder 1 is regulated at 280° C.** Extruder 1 is regulated at 250° C.

These experiments demonstrate that it is advisable to use a polyamidepossessing a conversion temperature of less than 230° C. in order toprovide correct processing by coextrusion blow-moulding.

Examples 4 to 7

The alloys of polyamide and of polyolefin collated in the tables belowwere prepared: Composition: Alloy 4 Alloy 5 Alloy 6 Alloy 7 PA A1 50 50PA A2 71 60 PEl 25 15 15 15 P1 4 35 29 19 P2 6 6

Examples 8 to 11

4 five-layer bottles, the structures of which are collated in the tablebelow, were extruded blow-moulded on the Bekum extrusion line. Example 8Example 9 Example 10 Example 11 Alloy 4 Alloy 5 Alloy 6 Alloy 7 T1 T1 T1T1 EVOH EVOH EVOH EVOH T1 T1 T1 T1 Structure PE2 PE2 PE2 PE2 Quality ofthe Correct Lack of Lack of Correct coextrusion coextrusion coextrusionImpact strength No* Yes** Yes Yes*”No” means that the value of the impact strength measured is less than50 J**“Yes” means that the value of the impact strength measured exceeds 50J

Examples 12 to 17

The alloys of polyamide and of polyolefin collated in the tables belowwere prepared: Alloy Alloy Alloy Alloy Alloy Alloy Comp. 12 13 14 15 1617 PA A3 PA A4 60 PA A5 60 PA A6 60 PA A7 60 PA A8 60 PE 1 60 P 1 15 1515 15 15 15 P 2 19 19 19 19 19 19 6 6 6 6 6 6

Examples 18 to 22

6 five-layer bottles, the structures of which are collated in the tablebelow, were extruded blow-moulded on the Bekum extrusion line. Example17 Example 18 Example 19 Example 20 Example 21 Example 22 Alloy 12 Alloy13 Alloy 14 Alloy 15 Alloy 16 Alloy 17 T1 T1 T1 T1 T1 T1 EVOH EVOH EVOHEVOH EVOH EVOH T1 T1 T1 T1 T1 T1 Structure PE2 PE2 PE2 PE2 PE2 PE2Quality of the Correct Correct Correct Correct Correct Correctcoextrusion Impact Yes* Yes Yes Yes Yes Yes strength*“Yes” means that the value of the impact strength measured exceeds 50 J

1. A structure comprising in order: a) a first layer of high densitypolyethylene (HDPE), b) a tie layer, c) a second layer of EVOH or of ablend based on EVOH, d) optionally a tie layer, e) a third layer of ablend comprising, by weight, the total being 100%: 50 to 90% ofpolyamide (A) having a conversion temperature of at most 230° C., 1 to30% of high density polyethylene (HDPE), 5 to 30% of an impact modifierchosen from elastomers and very low density polyethylenes, wherein theHDPE and/or the impact modifier is functionalized, in whole or in part,wherein the layers are coextrudable.
 2. The structure according to claim1, wherein said polyamide (A) is polyamide 6/6-6 or polyamide 6/12. 3.The structure according to claim 1, wherein the proportion offunctionalized HDPE and/or of functionalized modifier with respect tothe combined functionalized or nonfunctionalized HDPE and functionalizedor nonfunctionalized impact modifier in the third layer (e) is between 0and 70 percent by weight.
 4. The structure according to claim 3, whereinthe proportion of functionalized HDPE and/or of functionalized modifierwith respect to the combined functionalized or nonfunctionalized HDPEand functionalized or nonfunctionalized impact modifier in the thirdlayer (e) is between 5 and 60 percent by weight.
 5. The structureaccording to claim 4, in which the proportion of functionalized HDPEand/or of fuctionalized modifier with respect to the combinedfunctionalized or nonfunctionalized HDPE and functionalized ornonfunctionalized impact modifier in the third layer (e) is between 20and 60 percent by weight.
 6. The structure according to claim 1, whereinin layer (e) the HDPE is not functionalized and the impact modifier isfunctionalized in all or part.
 7. The structure according to claim 1,wherein the impact modifier is an ethylene-propylene rubber (EPR) or anethylene-propylene-diene monomer elastomer (EPDM).
 8. The structureaccording to claim 1, wherein the functionalized impact modifier is anEPR or an EPDM grafted by maleic anhydride.
 9. The structure accordingto claim 1, wherein the proportions of the blend of the third layer are,the total being 100%: 55 to 80% of polyamide (A), 10 to 20% of highdensity polyethylene (HDPE), 10 to 30% of impact modifier.
 10. Thestructure according to claim 1, in which a layer of recycled polymers ispositioned between the first layer and the tie layer.
 11. The structureaccording to claim 10, in which the layer of recycled polymers furthercomprises HDPE and/or functionalized polyolefins.
 12. A devices for thetransfer or storage of fluids comprising the structure according toclaim 1, in which the third layer (e) is in direct contact with thefluid present or transported.
 13. The device according to claim 12wherein said device is selected from the group consisting of a pipe, atank, a conduit, a bottle, and a container.